This invention relates to technology for reducing the amount of Fe3O4 in slag having a specific gravity of about 3.5-4.0, and in the intermediate layer between the slag and matte, the intermediate layer having a specific gravity of 4.0-5.0, in the setting area of copper smelting. furnace.
Normally, in a copper smelting furnace, pulverized raw copper concentrate and silica sand are blown into the reaction shaft of the furnace along with auxiliary fuel and oxygen-enriched air, and oxidation takes place either in a gaseous-solid state or a gaseous-liquid-solid state. The product of oxidation consists of the matte, in which valuable metals such as copper are condensed, and the slag, which is produced by the slag-making reaction between FeO (produced when iron reacts with oxygen) and SiO2. These are segregated by settling in a receptacle. The slag layer, which has a lower specific gravity, settles at the upper portion of the receptacle, while the matte layer settles in the lower portion.
During the reaction described above, oxygen-enriched air can be applied to the raw copper concentrate at a proportion in excess of or at a proportion less than the desired level, thereby causing variations in the reaction process. In the former case, the oxidation of iron within the raw material proceeds too rapidly, causing a portion of the Fe to oxidize excessively from FeO wherein Fe has an oxidation-reduction number of 2+ to Fe3O4 wherein the Fe has an oxidation-reduction number of 3+. Because Fe3O4 has a high melting point, the increase in the proportion of Fe3O4 within the slag increases its viscosity.
In addition, Fe3O4 has a high specific gravity and forms a layer beneath the slag layer which is fused to the slag. If the proportion of Fe3O4 is high enough, this layer becomes clearly distinguishable from the slag layer. Since this layer is situated in the middle of the slag layer and the matte layer, it is known as the xe2x80x9cintermediate layer.xe2x80x9d As stated before, an increase in the production of Fe3O4 as a result of variations in the reaction process leads to an increase in the thickness of the intermediate layer, which interferes with the segregation of valuable metals drifting within the slag layer.
In addition, oxidized matter formed excessively during variations in the reaction can turn into powdered dust, which can be pulled into the exhaust gas and drawn into the gas exhaust openings, creating accretion, part of which can then be retained and sink to the bottom of the receptacle, creating a buildup that lessens the holding capacity of the receptacle.
Thus, as described above, production of Fe3O4 resulting from variations in the reaction can cause loss of valuable metal drifting within the slag layer and difficulties in closing the slag tap hole, as well as affect the temperature of the slag and the matte and the quantity of the valuable metal in the matte layer, thus causing undesirable effects in later processes.
Hence, there was a need to find a method to deoxidize the Fe3O4 within the slag and the intermediate layers to FeO, thus decreasing the viscosity of the slag and reducing the amount of Fe3O4 within the intermediate layer.
Previously, the Fe3O4 at the lower portion of the receptacle was deoxidized to FeO by introducing blocks of pig iron (ingots shaped 280 mm Lxc3x9780 mm Wxc3x9750 mm H, 5 kgs in weight, specific gravity of 7.0 to 7.8) from the upper portion of the receptacle and allowing them to sink to the bottom. However, with this method, the pig iron block does not remain in the slag and intermediate layers but sinks to the bottom of the receptacle, and thus is not effective in deoxidizing Fe3O4 in these layers. The present invention is based upon a relation between specific gravity and grain size of material effective for the deoxidization of Fe3O4 such that the material remains within the slag and the intermediate layers, whereby the deoxidization of Fe3O4 is effected.
The present invention comprises a method of operating a copper smelting furnace wherein a ferrous substance containing more than 80 wt. % metallic iron, having a specific gravity of 3.0-8.0 and particle diameter of 0.3-15.0 mm, is added to copper smelting slag. The ferrous substance is added to the Fe3O4 in the intermediate layer, thereby deoxidizing the Fe3O4 to FeO. More specifically, the present invention comprises a method of operating a copper smelting furnace wherein the ferrous substance specified above is added to the intermediate layer generated between the slag and the matte so as to reduce said intermediate layer.
By employing the present invention, it is possible to reduce the amount of Fe3O4 within the slag layer and intermediate layer through the simple method of adding grain-shaped matter from above. This allows valuable metals, such as copper, gold and silver drifting within the slag to sink more rapidly, thereby increasing their recovery rate. In addition, various problems in the intermediate layer are reduced, thereby allowing for more efficient operation of the copper smelting furnace.